1. Field of the Invention
The present invention relates to a sheet feeding apparatus provided with a size detecting portion configured to detect a size of a sheet, and an image forming apparatus including the sheet feeding apparatus.
2. Description of the Related Art
Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile, and a multifunction printer having combined functions thereof, a sheet feeding apparatus configured to feed a sheet to an image forming portion is provided. The sheet feeding apparatus is provided with a sheet feeding cassette capable of containing various sizes of sheets. In order to form an image at an appropriate position on the sheet fed from the sheet feeding cassette, the size of the sheet contained in the sheet feeding cassette is required to be discriminated in advance by a control device installed in an apparatus main body of the image forming apparatus.
In this regard, as described in Japanese Patent Application Laid-Open No. 2002-321848, there is proposed an image forming apparatus in which a size detecting portion for transmitting a signal of size information according to the size of a sheet to the control device is provided in order that the control device is capable of discriminating the size of the sheet contained in the sheet feeding cassette. The sheet feeding cassette of this type of the image forming apparatus includes a cassette body and a regulation plate for regulating side edges in the width direction of the sheet. Further, the size detecting portion includes a size detecting lever (cam), which is arranged on an apparatus main body side, and pivots while coming into sliding contact with the regulation plate, and a plurality of detection elements (sensors or switches) selectively turned ON and OFF according to a pivotal position of the size detecting lever.
With this structure, when the regulation plate is moved along the side edge of the sheet contained in the sheet feeding cassette, the size detecting lever pivots in association with the movement of the regulation plate. In this state, when the sheet feeding cassette is mounted in the apparatus main body, according to the pivotal position of the size detecting lever, the size detecting lever selectively turns ON and OFF the plurality of detection elements arranged in the apparatus main body. Then, a signal representing a combination of ON and OFF of the detection elements is sent to the control device. The control device is capable of discriminating the size of the sheet contained in the sheet feeding cassette based on the signal.
Incidentally, the size of the sheet to be contained in the sheet feeding cassette is limited to some extent in the conventional sheet feeding apparatus. Therefore, in recent years, there is a demand for a sheet feeding apparatus adaptable to various sizes of sheets including a small size and a large size.
However, as the size of the sheet contained in the sheet feeding cassette becomes large, a regulation position of the regulation plate gets closer to a pivot supporting point of the size detecting lever, and hence a pivotal amount of the size detecting lever with respect to a moving amount of the regulation plate becomes small. Further, when the difference in size between the various sheets becomes small, the difference in moving amount of the regulation plate becomes small, and hence the pivotal amount of the size detecting lever coming into sliding contact with the regulation plate becomes small.
When the pivotal amount of the size detecting lever thus becomes small, there is fear that ON and OFF of the detection elements are not switched according to the size of the sheet, and hence discrimination of the size of the sheet becomes difficult. That is, there is fear that the control device makes erroneous discrimination of the size without properly detecting the size of the sheet.
Then, when the size of the sheet is erroneously detected, the size of the detected sheet is different from the size of the sheet actually contained in the sheet feeding cassette. Therefore, there is fear that operation of the image forming apparatus becomes unstable as exemplified by occurrence of sheet jamming. Accordingly, there is a need for improving detection accuracy of the size of the sheet.